13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
28 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
29 #include "gc/shenandoah/shenandoahControlThread.hpp"
30 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
31 #include "gc/shenandoah/shenandoahFreeSet.hpp"
32 #include "gc/shenandoah/shenandoahFullGC.hpp"
33 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahMark.inline.hpp"
36 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
37 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
38 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
39 #include "gc/shenandoah/shenandoahUtils.hpp"
40 #include "gc/shenandoah/shenandoahVMOperations.hpp"
41 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
42 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
43 #include "memory/iterator.hpp"
44 #include "memory/metaspaceUtils.hpp"
45 #include "memory/metaspaceStats.hpp"
46 #include "memory/universe.hpp"
47 #include "runtime/atomic.hpp"
48
49 ShenandoahControlThread::ShenandoahControlThread() :
50 ConcurrentGCThread(),
51 _alloc_failure_waiters_lock(Mutex::safepoint-1, "ShenandoahAllocFailureGC_lock", true),
52 _gc_waiters_lock(Mutex::safepoint-1, "ShenandoahRequestedGC_lock", true),
53 _periodic_task(this),
54 _requested_gc_cause(GCCause::_no_cause_specified),
55 _degen_point(ShenandoahGC::_degenerated_outside_cycle),
56 _allocs_seen(0) {
57
58 reset_gc_id();
59 create_and_start();
60 _periodic_task.enroll();
61 if (ShenandoahPacing) {
62 _periodic_pacer_notify_task.enroll();
63 }
64 }
65
66 ShenandoahControlThread::~ShenandoahControlThread() {
67 // This is here so that super is called.
68 }
69
70 void ShenandoahPeriodicTask::task() {
71 _thread->handle_force_counters_update();
72 _thread->handle_counters_update();
73 }
74
75 void ShenandoahPeriodicPacerNotify::task() {
76 assert(ShenandoahPacing, "Should not be here otherwise");
77 ShenandoahHeap::heap()->pacer()->notify_waiters();
78 }
79
80 void ShenandoahControlThread::run_service() {
81 ShenandoahHeap* heap = ShenandoahHeap::heap();
82
83 GCMode default_mode = concurrent_normal;
84 GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
85 int sleep = ShenandoahControlIntervalMin;
86
87 double last_shrink_time = os::elapsedTime();
88 double last_sleep_adjust_time = os::elapsedTime();
89
90 // Shrink period avoids constantly polling regions for shrinking.
91 // Having a period 10x lower than the delay would mean we hit the
92 // shrinking with lag of less than 1/10-th of true delay.
93 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
94 double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
95
96 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
97 ShenandoahHeuristics* heuristics = heap->heuristics();
98 while (!in_graceful_shutdown() && !should_terminate()) {
99 // Figure out if we have pending requests.
100 bool alloc_failure_pending = _alloc_failure_gc.is_set();
101 bool is_gc_requested = _gc_requested.is_set();
102 GCCause::Cause requested_gc_cause = _requested_gc_cause;
103 bool explicit_gc_requested = is_gc_requested && is_explicit_gc(requested_gc_cause);
104 bool implicit_gc_requested = is_gc_requested && !is_explicit_gc(requested_gc_cause);
105
106 // This control loop iteration have seen this much allocations.
107 size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
108
109 // Check if we have seen a new target for soft max heap size.
110 bool soft_max_changed = check_soft_max_changed();
111
112 // Choose which GC mode to run in. The block below should select a single mode.
113 GCMode mode = none;
114 GCCause::Cause cause = GCCause::_last_gc_cause;
115 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
116
117 if (alloc_failure_pending) {
118 // Allocation failure takes precedence: we have to deal with it first thing
119 log_info(gc)("Trigger: Handle Allocation Failure");
120
121 cause = GCCause::_allocation_failure;
122
123 // Consume the degen point, and seed it with default value
124 degen_point = _degen_point;
125 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
126
127 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
128 heuristics->record_allocation_failure_gc();
129 policy->record_alloc_failure_to_degenerated(degen_point);
130 mode = stw_degenerated;
131 } else {
132 heuristics->record_allocation_failure_gc();
133 policy->record_alloc_failure_to_full();
134 mode = stw_full;
135 }
136
137 } else if (explicit_gc_requested) {
138 cause = requested_gc_cause;
139 log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
140
141 heuristics->record_requested_gc();
142
143 if (ExplicitGCInvokesConcurrent) {
144 policy->record_explicit_to_concurrent();
145 mode = default_mode;
146 // Unload and clean up everything
147 heap->set_unload_classes(heuristics->can_unload_classes());
148 } else {
149 policy->record_explicit_to_full();
150 mode = stw_full;
151 }
152 } else if (implicit_gc_requested) {
153 cause = requested_gc_cause;
154 log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
155
156 heuristics->record_requested_gc();
157
158 if (ShenandoahImplicitGCInvokesConcurrent) {
159 policy->record_implicit_to_concurrent();
160 mode = default_mode;
161
162 // Unload and clean up everything
163 heap->set_unload_classes(heuristics->can_unload_classes());
164 } else {
165 policy->record_implicit_to_full();
166 mode = stw_full;
167 }
168 } else {
169 // Potential normal cycle: ask heuristics if it wants to act
170 if (heuristics->should_start_gc()) {
171 mode = default_mode;
172 cause = default_cause;
173 }
174
175 // Ask policy if this cycle wants to process references or unload classes
176 heap->set_unload_classes(heuristics->should_unload_classes());
177 }
178
179 // Blow all soft references on this cycle, if handling allocation failure,
180 // either implicit or explicit GC request, or we are requested to do so unconditionally.
181 if (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs) {
182 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
183 }
184
185 bool gc_requested = (mode != none);
186 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
187
188 if (gc_requested) {
189 // GC is starting, bump the internal ID
190 update_gc_id();
191
192 heap->reset_bytes_allocated_since_gc_start();
193
194 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
195
196 // If GC was requested, we are sampling the counters even without actual triggers
197 // from allocation machinery. This captures GC phases more accurately.
198 set_forced_counters_update(true);
199
200 // If GC was requested, we better dump freeset data for performance debugging
201 {
202 ShenandoahHeapLocker locker(heap->lock());
203 heap->free_set()->log_status();
204 }
205
206 switch (mode) {
207 case concurrent_normal:
208 service_concurrent_normal_cycle(cause);
209 break;
210 case stw_degenerated:
211 service_stw_degenerated_cycle(cause, degen_point);
212 break;
213 case stw_full:
214 service_stw_full_cycle(cause);
215 break;
216 default:
217 ShouldNotReachHere();
218 }
219
220 // If this was the requested GC cycle, notify waiters about it
221 if (explicit_gc_requested || implicit_gc_requested) {
222 notify_gc_waiters();
223 }
224
225 // If this was the allocation failure GC cycle, notify waiters about it
226 if (alloc_failure_pending) {
227 notify_alloc_failure_waiters();
228 }
229
230 // Report current free set state at the end of cycle, whether
231 // it is a normal completion, or the abort.
232 {
233 ShenandoahHeapLocker locker(heap->lock());
234 heap->free_set()->log_status();
235
236 // Notify Universe about new heap usage. This has implications for
237 // global soft refs policy, and we better report it every time heap
238 // usage goes down.
239 Universe::heap()->update_capacity_and_used_at_gc();
240
241 // Signal that we have completed a visit to all live objects.
242 Universe::heap()->record_whole_heap_examined_timestamp();
243 }
244
245 // Disable forced counters update, and update counters one more time
246 // to capture the state at the end of GC session.
247 handle_force_counters_update();
248 set_forced_counters_update(false);
249
250 // Retract forceful part of soft refs policy
251 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
252
253 // Clear metaspace oom flag, if current cycle unloaded classes
254 if (heap->unload_classes()) {
255 heuristics->clear_metaspace_oom();
256 }
257
258 // Commit worker statistics to cycle data
259 heap->phase_timings()->flush_par_workers_to_cycle();
260 if (ShenandoahPacing) {
261 heap->pacer()->flush_stats_to_cycle();
262 }
263
264 // Print GC stats for current cycle
265 {
266 LogTarget(Info, gc, stats) lt;
267 if (lt.is_enabled()) {
268 ResourceMark rm;
269 LogStream ls(lt);
270 heap->phase_timings()->print_cycle_on(&ls);
271 if (ShenandoahPacing) {
272 heap->pacer()->print_cycle_on(&ls);
273 }
274 }
275 }
276
277 // Commit statistics to globals
278 heap->phase_timings()->flush_cycle_to_global();
279
280 // Print Metaspace change following GC (if logging is enabled).
281 MetaspaceUtils::print_metaspace_change(meta_sizes);
282
283 // GC is over, we are at idle now
284 if (ShenandoahPacing) {
285 heap->pacer()->setup_for_idle();
286 }
287 } else {
288 // Allow allocators to know we have seen this much regions
289 if (ShenandoahPacing && (allocs_seen > 0)) {
290 heap->pacer()->report_alloc(allocs_seen);
291 }
292 }
293
294 double current = os::elapsedTime();
295
296 if (ShenandoahUncommit && (explicit_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
297 // Explicit GC tries to uncommit everything down to min capacity.
298 // Soft max change tries to uncommit everything down to target capacity.
299 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
300
301 double shrink_before = (explicit_gc_requested || soft_max_changed) ?
302 current :
303 current - (ShenandoahUncommitDelay / 1000.0);
304
305 size_t shrink_until = soft_max_changed ?
306 heap->soft_max_capacity() :
307 heap->min_capacity();
308
309 service_uncommit(shrink_before, shrink_until);
310 heap->phase_timings()->flush_cycle_to_global();
311 last_shrink_time = current;
312 }
313
314 // Wait before performing the next action. If allocation happened during this wait,
315 // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
316 // back off exponentially.
317 if (_heap_changed.try_unset()) {
318 sleep = ShenandoahControlIntervalMin;
319 } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
320 sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
321 last_sleep_adjust_time = current;
322 }
323 os::naked_short_sleep(sleep);
324 }
325
326 // Wait for the actual stop(), can't leave run_service() earlier.
327 while (!should_terminate()) {
328 os::naked_short_sleep(ShenandoahControlIntervalMin);
329 }
330 }
331
332 bool ShenandoahControlThread::check_soft_max_changed() const {
333 ShenandoahHeap* heap = ShenandoahHeap::heap();
334 size_t new_soft_max = Atomic::load(&SoftMaxHeapSize);
335 size_t old_soft_max = heap->soft_max_capacity();
336 if (new_soft_max != old_soft_max) {
337 new_soft_max = MAX2(heap->min_capacity(), new_soft_max);
338 new_soft_max = MIN2(heap->max_capacity(), new_soft_max);
339 if (new_soft_max != old_soft_max) {
340 log_info(gc)("Soft Max Heap Size: " SIZE_FORMAT "%s -> " SIZE_FORMAT "%s",
341 byte_size_in_proper_unit(old_soft_max), proper_unit_for_byte_size(old_soft_max),
342 byte_size_in_proper_unit(new_soft_max), proper_unit_for_byte_size(new_soft_max)
343 );
344 heap->set_soft_max_capacity(new_soft_max);
345 return true;
346 }
347 }
348 return false;
349 }
350
351 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
352 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
353 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
354 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
355 // tries to evac something and no memory is available), cycle degrades to Full GC.
356 //
357 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
358 // heuristics says there are no regions to compact, and all the collection comes from immediately
359 // reclaimable regions.
360 //
361 // ................................................................................................
362 //
363 // (immediate garbage shortcut) Concurrent GC
364 // /-------------------------------------------\
365 // | |
366 // | |
367 // | |
368 // | v
369 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
370 // | | | ^
371 // | (af) | (af) | (af) |
372 // ..................|....................|.................|..............|.......................
373 // | | | |
374 // | | | | Degenerated GC
375 // v v v |
376 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
377 // | | | ^
378 // | (af) | (af) | (af) |
379 // ..................|....................|.................|..............|.......................
380 // | | | |
381 // | v | | Full GC
382 // \------------------->o<----------------/ |
383 // | |
384 // v |
385 // Full GC --------------------------/
386 //
387 ShenandoahHeap* heap = ShenandoahHeap::heap();
388 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
389
390 GCIdMark gc_id_mark;
391 ShenandoahGCSession session(cause);
392
393 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
394
395 ShenandoahConcurrentGC gc;
396 if (gc.collect(cause)) {
397 // Cycle is complete
398 heap->heuristics()->record_success_concurrent();
399 heap->shenandoah_policy()->record_success_concurrent();
400 } else {
401 assert(heap->cancelled_gc(), "Must have been cancelled");
402 check_cancellation_or_degen(gc.degen_point());
403 }
404 }
405
406 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
407 ShenandoahHeap* heap = ShenandoahHeap::heap();
408 if (heap->cancelled_gc()) {
409 assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
410 if (!in_graceful_shutdown()) {
411 assert (_degen_point == ShenandoahGC::_degenerated_outside_cycle,
412 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
413 _degen_point = point;
414 }
415 return true;
416 }
417 return false;
418 }
419
420 void ShenandoahControlThread::stop_service() {
421 // Nothing to do here.
422 }
423
424 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
425 GCIdMark gc_id_mark;
426 ShenandoahGCSession session(cause);
427
428 ShenandoahFullGC gc;
429 gc.collect(cause);
430
431 ShenandoahHeap* const heap = ShenandoahHeap::heap();
432 heap->heuristics()->record_success_full();
433 heap->shenandoah_policy()->record_success_full();
434 }
435
436 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
437 assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
438
439 GCIdMark gc_id_mark;
440 ShenandoahGCSession session(cause);
441
442 ShenandoahDegenGC gc(point);
443 gc.collect(cause);
444
445 ShenandoahHeap* const heap = ShenandoahHeap::heap();
446 heap->heuristics()->record_success_degenerated();
447 heap->shenandoah_policy()->record_success_degenerated();
448 }
449
450 void ShenandoahControlThread::service_uncommit(double shrink_before, size_t shrink_until) {
451 ShenandoahHeap* heap = ShenandoahHeap::heap();
452
453 // Determine if there is work to do. This avoids taking heap lock if there is
454 // no work available, avoids spamming logs with superfluous logging messages,
455 // and minimises the amount of work while locks are taken.
456
457 if (heap->committed() <= shrink_until) return;
458
459 bool has_work = false;
460 for (size_t i = 0; i < heap->num_regions(); i++) {
461 ShenandoahHeapRegion *r = heap->get_region(i);
462 if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
463 has_work = true;
464 break;
465 }
466 }
467
468 if (has_work) {
469 heap->entry_uncommit(shrink_before, shrink_until);
470 }
471 }
472
473 bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
474 return GCCause::is_user_requested_gc(cause) ||
475 GCCause::is_serviceability_requested_gc(cause);
476 }
477
478 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
479 assert(GCCause::is_user_requested_gc(cause) ||
480 GCCause::is_serviceability_requested_gc(cause) ||
481 cause == GCCause::_metadata_GC_clear_soft_refs ||
482 cause == GCCause::_codecache_GC_threshold ||
483 cause == GCCause::_full_gc_alot ||
484 cause == GCCause::_wb_full_gc ||
485 cause == GCCause::_wb_breakpoint ||
486 cause == GCCause::_scavenge_alot,
487 "only requested GCs here");
488
489 if (is_explicit_gc(cause)) {
490 if (!DisableExplicitGC) {
491 handle_requested_gc(cause);
492 }
493 } else {
494 handle_requested_gc(cause);
495 }
496 }
497
498 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
499 // Make sure we have at least one complete GC cycle before unblocking
500 // from the explicit GC request.
501 //
502 // This is especially important for weak references cleanup and/or native
503 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
504 // comes very late in the already running cycle, it would miss lots of new
505 // opportunities for cleanup that were made available before the caller
506 // requested the GC.
507
508 MonitorLocker ml(&_gc_waiters_lock);
509 size_t current_gc_id = get_gc_id();
510 size_t required_gc_id = current_gc_id + 1;
511 while (current_gc_id < required_gc_id) {
512 // Although setting gc request is under _gc_waiters_lock, but read side (run_service())
513 // does not take the lock. We need to enforce following order, so that read side sees
514 // latest requested gc cause when the flag is set.
515 _requested_gc_cause = cause;
516 _gc_requested.set();
517
518 if (cause != GCCause::_wb_breakpoint) {
519 ml.wait();
520 }
521 current_gc_id = get_gc_id();
522 }
523 }
524
525 void ShenandoahControlThread::handle_alloc_failure(ShenandoahAllocRequest& req) {
526 ShenandoahHeap* heap = ShenandoahHeap::heap();
527
528 assert(current()->is_Java_thread(), "expect Java thread here");
529
530 if (try_set_alloc_failure_gc()) {
531 // Only report the first allocation failure
532 log_info(gc)("Failed to allocate %s, " SIZE_FORMAT "%s",
533 req.type_string(),
534 byte_size_in_proper_unit(req.size() * HeapWordSize), proper_unit_for_byte_size(req.size() * HeapWordSize));
535
536 // Now that alloc failure GC is scheduled, we can abort everything else
537 heap->cancel_gc(GCCause::_allocation_failure);
581 _do_counters_update.unset();
582 ShenandoahHeap::heap()->monitoring_support()->update_counters();
583 }
584 }
585
586 void ShenandoahControlThread::handle_force_counters_update() {
587 if (_force_counters_update.is_set()) {
588 _do_counters_update.unset(); // reset these too, we do update now!
589 ShenandoahHeap::heap()->monitoring_support()->update_counters();
590 }
591 }
592
593 void ShenandoahControlThread::notify_heap_changed() {
594 // This is called from allocation path, and thus should be fast.
595
596 // Update monitoring counters when we took a new region. This amortizes the
597 // update costs on slow path.
598 if (_do_counters_update.is_unset()) {
599 _do_counters_update.set();
600 }
601 // Notify that something had changed.
602 if (_heap_changed.is_unset()) {
603 _heap_changed.set();
604 }
605 }
606
607 void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
608 assert(ShenandoahPacing, "should only call when pacing is enabled");
609 Atomic::add(&_allocs_seen, words, memory_order_relaxed);
610 }
611
612 void ShenandoahControlThread::set_forced_counters_update(bool value) {
613 _force_counters_update.set_cond(value);
614 }
615
616 void ShenandoahControlThread::reset_gc_id() {
617 Atomic::store(&_gc_id, (size_t)0);
618 }
619
620 void ShenandoahControlThread::update_gc_id() {
621 Atomic::inc(&_gc_id);
622 }
623
624 size_t ShenandoahControlThread::get_gc_id() {
629 print_on(tty);
630 }
631
632 void ShenandoahControlThread::print_on(outputStream* st) const {
633 st->print("Shenandoah Concurrent Thread");
634 Thread::print_on(st);
635 st->cr();
636 }
637
638 void ShenandoahControlThread::start() {
639 create_and_start();
640 }
641
642 void ShenandoahControlThread::prepare_for_graceful_shutdown() {
643 _graceful_shutdown.set();
644 }
645
646 bool ShenandoahControlThread::in_graceful_shutdown() {
647 return _graceful_shutdown.is_set();
648 }
|
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
28 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
29 #include "gc/shenandoah/shenandoahControlThread.hpp"
30 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
31 #include "gc/shenandoah/shenandoahFreeSet.hpp"
32 #include "gc/shenandoah/shenandoahFullGC.hpp"
33 #include "gc/shenandoah/shenandoahGeneration.hpp"
34 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
35 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
36 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
37 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
38 #include "gc/shenandoah/shenandoahMark.inline.hpp"
39 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
40 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
41 #include "gc/shenandoah/shenandoahOldGC.hpp"
42 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
43 #include "gc/shenandoah/shenandoahUtils.hpp"
44 #include "gc/shenandoah/shenandoahVMOperations.hpp"
45 #include "gc/shenandoah/shenandoahWorkerPolicy.hpp"
46 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
47 #include "gc/shenandoah/mode/shenandoahMode.hpp"
48 #include "memory/iterator.hpp"
49 #include "memory/metaspaceUtils.hpp"
50 #include "memory/metaspaceStats.hpp"
51 #include "memory/universe.hpp"
52 #include "runtime/atomic.hpp"
53
54 ShenandoahControlThread::ShenandoahControlThread() :
55 ConcurrentGCThread(),
56 _alloc_failure_waiters_lock(Mutex::safepoint - 1, "ShenandoahAllocFailureGC_lock", true),
57 _gc_waiters_lock(Mutex::safepoint - 1, "ShenandoahRequestedGC_lock", true),
58 _control_lock(Mutex::nosafepoint - 1, "ShenandoahControlGC_lock", true),
59 _regulator_lock(Mutex::nosafepoint - 1, "ShenandoahRegulatorGC_lock", true),
60 _periodic_task(this),
61 _requested_gc_cause(GCCause::_no_cause_specified),
62 _requested_generation(GenerationMode::GLOBAL),
63 _degen_point(ShenandoahGC::_degenerated_outside_cycle),
64 _degen_generation(NULL),
65 _allocs_seen(0),
66 _mode(none) {
67
68 reset_gc_id();
69 create_and_start();
70 _periodic_task.enroll();
71 if (ShenandoahPacing) {
72 _periodic_pacer_notify_task.enroll();
73 }
74 }
75
76 ShenandoahControlThread::~ShenandoahControlThread() {
77 // This is here so that super is called.
78 }
79
80 void ShenandoahPeriodicTask::task() {
81 _thread->handle_force_counters_update();
82 _thread->handle_counters_update();
83 }
84
85 void ShenandoahPeriodicPacerNotify::task() {
86 assert(ShenandoahPacing, "Should not be here otherwise");
87 ShenandoahHeap::heap()->pacer()->notify_waiters();
88 }
89
90 void ShenandoahControlThread::run_service() {
91 ShenandoahHeap* heap = ShenandoahHeap::heap();
92
93 GCMode default_mode = concurrent_normal;
94 GenerationMode generation = GLOBAL;
95 GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
96
97 double last_shrink_time = os::elapsedTime();
98 uint age_period = 0;
99
100 // Shrink period avoids constantly polling regions for shrinking.
101 // Having a period 10x lower than the delay would mean we hit the
102 // shrinking with lag of less than 1/10-th of true delay.
103 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
104 double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
105
106 ShenandoahCollectorPolicy* policy = heap->shenandoah_policy();
107
108 // Heuristics are notified of allocation failures here and other outcomes
109 // of the cycle. They're also used here to control whether the Nth consecutive
110 // degenerated cycle should be 'promoted' to a full cycle. The decision to
111 // trigger a cycle or not is evaluated on the regulator thread.
112 ShenandoahHeuristics* global_heuristics = heap->global_generation()->heuristics();
113 while (!in_graceful_shutdown() && !should_terminate()) {
114 // Figure out if we have pending requests.
115 bool alloc_failure_pending = _alloc_failure_gc.is_set();
116 bool is_gc_requested = _gc_requested.is_set();
117 GCCause::Cause requested_gc_cause = _requested_gc_cause;
118 bool explicit_gc_requested = is_gc_requested && is_explicit_gc(requested_gc_cause);
119 bool implicit_gc_requested = is_gc_requested && is_implicit_gc(requested_gc_cause);
120
121 // This control loop iteration have seen this much allocations.
122 size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
123
124 // Check if we have seen a new target for soft max heap size.
125 bool soft_max_changed = check_soft_max_changed();
126
127 // Choose which GC mode to run in. The block below should select a single mode.
128 set_gc_mode(none);
129 GCCause::Cause cause = GCCause::_last_gc_cause;
130 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
131
132 if (alloc_failure_pending) {
133 // Allocation failure takes precedence: we have to deal with it first thing
134 log_info(gc)("Trigger: Handle Allocation Failure");
135
136 cause = GCCause::_allocation_failure;
137
138 // Consume the degen point, and seed it with default value
139 degen_point = _degen_point;
140 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
141
142 if (degen_point == ShenandoahGC::_degenerated_outside_cycle) {
143 _degen_generation = heap->mode()->is_generational() ? heap->young_generation() : heap->global_generation();
144 } else {
145 assert(_degen_generation != NULL, "Need to know which generation to resume.");
146 }
147
148 ShenandoahHeuristics* heuristics = _degen_generation->heuristics();
149 generation = _degen_generation->generation_mode();
150 bool old_gen_evacuation_failed = heap->clear_old_evacuation_failure();
151
152 // Do not bother with degenerated cycle if old generation evacuation failed.
153 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle() && !old_gen_evacuation_failed) {
154 heuristics->record_allocation_failure_gc();
155 policy->record_alloc_failure_to_degenerated(degen_point);
156 set_gc_mode(stw_degenerated);
157 } else {
158 heuristics->record_allocation_failure_gc();
159 policy->record_alloc_failure_to_full();
160 generation = GLOBAL;
161 set_gc_mode(stw_full);
162 }
163 } else if (explicit_gc_requested) {
164 cause = requested_gc_cause;
165 generation = GLOBAL;
166 log_info(gc)("Trigger: Explicit GC request (%s)", GCCause::to_string(cause));
167
168 global_heuristics->record_requested_gc();
169
170 if (ExplicitGCInvokesConcurrent) {
171 policy->record_explicit_to_concurrent();
172 set_gc_mode(default_mode);
173 // Unload and clean up everything
174 heap->set_unload_classes(global_heuristics->can_unload_classes());
175 } else {
176 policy->record_explicit_to_full();
177 set_gc_mode(stw_full);
178 }
179 } else if (implicit_gc_requested) {
180 cause = requested_gc_cause;
181 generation = GLOBAL;
182 log_info(gc)("Trigger: Implicit GC request (%s)", GCCause::to_string(cause));
183
184 global_heuristics->record_requested_gc();
185
186 if (ShenandoahImplicitGCInvokesConcurrent) {
187 policy->record_implicit_to_concurrent();
188 set_gc_mode(default_mode);
189
190 // Unload and clean up everything
191 heap->set_unload_classes(global_heuristics->can_unload_classes());
192 } else {
193 policy->record_implicit_to_full();
194 set_gc_mode(stw_full);
195 }
196 } else {
197 // We should only be here if the regulator requested a cycle or if
198 // there is an old generation mark in progress.
199 if (_requested_gc_cause == GCCause::_shenandoah_concurrent_gc) {
200 if (_requested_generation == OLD && heap->doing_mixed_evacuations()) {
201 // If a request to start an old cycle arrived while an old cycle was running, but _before_
202 // it chose any regions for evacuation we don't want to start a new old cycle. Rather, we want
203 // the heuristic to run a young collection so that we can evacuate some old regions.
204 assert(!heap->is_concurrent_old_mark_in_progress(), "Should not be running mixed collections and concurrent marking.");
205 generation = YOUNG;
206 } else {
207 generation = _requested_generation;
208 }
209
210 // preemption was requested or this is a regular cycle
211 cause = GCCause::_shenandoah_concurrent_gc;
212 set_gc_mode(default_mode);
213
214 // Don't start a new old marking if there is one already in progress.
215 if (generation == OLD && heap->is_concurrent_old_mark_in_progress()) {
216 set_gc_mode(servicing_old);
217 }
218
219 if (generation == GLOBAL) {
220 heap->set_unload_classes(global_heuristics->should_unload_classes());
221 } else {
222 heap->set_unload_classes(false);
223 }
224
225 // Don't want to spin in this loop and start a cycle every time, so
226 // clear requested gc cause. This creates a race with callers of the
227 // blocking 'request_gc' method, but there it loops and resets the
228 // '_requested_gc_cause' until a full cycle is completed.
229 _requested_gc_cause = GCCause::_no_gc;
230 } else if (heap->is_concurrent_old_mark_in_progress() || heap->is_prepare_for_old_mark_in_progress()) {
231 // Nobody asked us to do anything, but we have an old-generation mark or old-generation preparation for
232 // mixed evacuation in progress, so resume working on that.
233 log_info(gc)("Resume old gc: marking=%s, preparing=%s",
234 BOOL_TO_STR(heap->is_concurrent_old_mark_in_progress()),
235 BOOL_TO_STR(heap->is_prepare_for_old_mark_in_progress()));
236
237 cause = GCCause::_shenandoah_concurrent_gc;
238 generation = OLD;
239 set_gc_mode(servicing_old);
240 }
241 }
242
243 // Blow all soft references on this cycle, if handling allocation failure,
244 // either implicit or explicit GC request, or we are requested to do so unconditionally.
245 if (generation == GLOBAL && (alloc_failure_pending || implicit_gc_requested || explicit_gc_requested || ShenandoahAlwaysClearSoftRefs)) {
246 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
247 }
248
249 bool gc_requested = (_mode != none);
250 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
251
252 if (gc_requested) {
253 // GC is starting, bump the internal ID
254 update_gc_id();
255
256 heap->reset_bytes_allocated_since_gc_start();
257
258 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
259
260 // If GC was requested, we are sampling the counters even without actual triggers
261 // from allocation machinery. This captures GC phases more accurately.
262 set_forced_counters_update(true);
263
264 // If GC was requested, we better dump freeset data for performance debugging
265 {
266 ShenandoahHeapLocker locker(heap->lock());
267 heap->free_set()->log_status();
268 }
269
270 heap->set_aging_cycle(false);
271 {
272 switch (_mode) {
273 case concurrent_normal: {
274 if ((generation == YOUNG) && (age_period-- == 0)) {
275 heap->set_aging_cycle(true);
276 age_period = ShenandoahAgingCyclePeriod - 1;
277 }
278 service_concurrent_normal_cycle(heap, generation, cause);
279 break;
280 }
281 case stw_degenerated: {
282 if (!service_stw_degenerated_cycle(cause, degen_point)) {
283 // The degenerated GC was upgraded to a Full GC
284 generation = GLOBAL;
285 }
286 break;
287 }
288 case stw_full: {
289 service_stw_full_cycle(cause);
290 break;
291 }
292 case servicing_old: {
293 assert(generation == OLD, "Expected old generation here");
294 service_concurrent_old_cycle(heap, cause);
295 break;
296 }
297 default: {
298 ShouldNotReachHere();
299 }
300 }
301 }
302
303 // If this was the requested GC cycle, notify waiters about it
304 if (explicit_gc_requested || implicit_gc_requested) {
305 notify_gc_waiters();
306 }
307
308 // If this was the allocation failure GC cycle, notify waiters about it
309 if (alloc_failure_pending) {
310 notify_alloc_failure_waiters();
311 }
312
313 // Report current free set state at the end of cycle, whether
314 // it is a normal completion, or the abort.
315 {
316 ShenandoahHeapLocker locker(heap->lock());
317 heap->free_set()->log_status();
318
319 // Notify Universe about new heap usage. This has implications for
320 // global soft refs policy, and we better report it every time heap
321 // usage goes down.
322 Universe::heap()->update_capacity_and_used_at_gc();
323
324 // Signal that we have completed a visit to all live objects.
325 Universe::heap()->record_whole_heap_examined_timestamp();
326 }
327
328 // Disable forced counters update, and update counters one more time
329 // to capture the state at the end of GC session.
330 handle_force_counters_update();
331 set_forced_counters_update(false);
332
333 // Retract forceful part of soft refs policy
334 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
335
336 // Clear metaspace oom flag, if current cycle unloaded classes
337 if (heap->unload_classes()) {
338 assert(generation == GLOBAL, "Only unload classes during GLOBAL cycle");
339 global_heuristics->clear_metaspace_oom();
340 }
341
342 process_phase_timings(heap);
343
344 // Print Metaspace change following GC (if logging is enabled).
345 MetaspaceUtils::print_metaspace_change(meta_sizes);
346
347 // GC is over, we are at idle now
348 if (ShenandoahPacing) {
349 heap->pacer()->setup_for_idle();
350 }
351 } else {
352 // Allow allocators to know we have seen this much regions
353 if (ShenandoahPacing && (allocs_seen > 0)) {
354 heap->pacer()->report_alloc(allocs_seen);
355 }
356 }
357
358 double current = os::elapsedTime();
359
360 if (ShenandoahUncommit && (explicit_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
361 // Explicit GC tries to uncommit everything down to min capacity.
362 // Soft max change tries to uncommit everything down to target capacity.
363 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
364
365 double shrink_before = (explicit_gc_requested || soft_max_changed) ?
366 current :
367 current - (ShenandoahUncommitDelay / 1000.0);
368
369 size_t shrink_until = soft_max_changed ?
370 heap->soft_max_capacity() :
371 heap->min_capacity();
372
373 service_uncommit(shrink_before, shrink_until);
374 heap->phase_timings()->flush_cycle_to_global();
375 last_shrink_time = current;
376 }
377
378 // Don't wait around if there was an allocation failure - start the next cycle immediately.
379 if (!is_alloc_failure_gc()) {
380 // The timed wait is necessary because this thread has a responsibility to send
381 // 'alloc_words' to the pacer when it does not perform a GC.
382 MonitorLocker lock(&_control_lock, Mutex::_no_safepoint_check_flag);
383 lock.wait(ShenandoahControlIntervalMax);
384 }
385 }
386
387 // Wait for the actual stop(), can't leave run_service() earlier.
388 while (!should_terminate()) {
389 os::naked_short_sleep(ShenandoahControlIntervalMin);
390 }
391 }
392
393 void ShenandoahControlThread::process_phase_timings(const ShenandoahHeap* heap) {
394
395 // Commit worker statistics to cycle data
396 heap->phase_timings()->flush_par_workers_to_cycle();
397 if (ShenandoahPacing) {
398 heap->pacer()->flush_stats_to_cycle();
399 }
400
401 // Print GC stats for current cycle
402 {
403 LogTarget(Info, gc, stats) lt;
404 if (lt.is_enabled()) {
405 ResourceMark rm;
406 LogStream ls(lt);
407 heap->phase_timings()->print_cycle_on(&ls);
408 if (ShenandoahPacing) {
409 heap->pacer()->print_cycle_on(&ls);
410 }
411 }
412 }
413
414 // Commit statistics to globals
415 heap->phase_timings()->flush_cycle_to_global();
416 }
417
418 // Young and old concurrent cycles are initiated by the regulator. Implicit
419 // and explicit GC requests are handled by the controller thread and always
420 // run a global cycle (which is concurrent by default, but may be overridden
421 // by command line options). Old cycles always degenerate to a global cycle.
422 // Young cycles are degenerated to complete the young cycle. Young
423 // and old degen may upgrade to Full GC. Full GC may also be
424 // triggered directly by a System.gc() invocation.
425 //
426 //
427 // +-----+ Idle +-----+-----------+---------------------+
428 // | + | | |
429 // | | | | |
430 // | | v | |
431 // | | Bootstrap Old +-- | ------------+ |
432 // | | + | | |
433 // | | | | | |
434 // | v v v v |
435 // | Resume Old <----------+ Young +--> Young Degen |
436 // | + + ^ + + |
437 // v | | | | | |
438 // Global <-+ | +----------------------------+ | |
439 // + | | |
440 // | v v |
441 // +---> Global Degen +--------------------> Full <----+
442 //
443 void ShenandoahControlThread::service_concurrent_normal_cycle(
444 const ShenandoahHeap* heap, const GenerationMode generation, GCCause::Cause cause) {
445
446 switch (generation) {
447 case YOUNG: {
448 // Run a young cycle. This might or might not, have interrupted an ongoing
449 // concurrent mark in the old generation. We need to think about promotions
450 // in this case. Promoted objects should be above the TAMS in the old regions
451 // they end up in, but we have to be sure we don't promote into any regions
452 // that are in the cset.
453 log_info(gc, ergo)("Start GC cycle (YOUNG)");
454 service_concurrent_cycle(heap->young_generation(), cause, false);
455 heap->young_generation()->log_status();
456 break;
457 }
458 case GLOBAL: {
459 log_info(gc, ergo)("Start GC cycle (GLOBAL)");
460 service_concurrent_cycle(heap->global_generation(), cause, false);
461 heap->global_generation()->log_status();
462 break;
463 }
464 case OLD: {
465 log_info(gc, ergo)("Start GC cycle (OLD)");
466 service_concurrent_old_cycle(heap, cause);
467 heap->old_generation()->log_status();
468 break;
469 }
470 default:
471 ShouldNotReachHere();
472 }
473 }
474
475 void ShenandoahControlThread::service_concurrent_old_cycle(const ShenandoahHeap* heap, GCCause::Cause &cause) {
476
477 ShenandoahOldGeneration* old_generation = heap->old_generation();
478 ShenandoahYoungGeneration* young_generation = heap->young_generation();
479
480 GCIdMark gc_id_mark;
481 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
482
483 switch (old_generation->state()) {
484 case ShenandoahOldGeneration::IDLE: {
485 assert(!heap->is_concurrent_old_mark_in_progress(), "Old already in progress.");
486 assert(old_generation->task_queues()->is_empty(), "Old mark queues should be empty.");
487 }
488 case ShenandoahOldGeneration::FILLING: {
489 _allow_old_preemption.set();
490 ShenandoahGCSession session(cause, old_generation);
491 old_generation->prepare_gc();
492 _allow_old_preemption.unset();
493
494 if (heap->is_prepare_for_old_mark_in_progress()) {
495 assert(old_generation->state() == ShenandoahOldGeneration::FILLING, "Prepare for mark should be in progress.");
496 return;
497 }
498
499 assert(old_generation->state() == ShenandoahOldGeneration::BOOTSTRAPPING, "Finished with filling, should be bootstrapping.");
500 }
501 case ShenandoahOldGeneration::BOOTSTRAPPING: {
502 // Configure the young generation's concurrent mark to put objects in
503 // old regions into the concurrent mark queues associated with the old
504 // generation. The young cycle will run as normal except that rather than
505 // ignore old references it will mark and enqueue them in the old concurrent
506 // task queues but it will not traverse them.
507 young_generation->set_old_gen_task_queues(old_generation->task_queues());
508 ShenandoahGCSession session(cause, young_generation);
509 service_concurrent_cycle(heap,young_generation, cause, true);
510 process_phase_timings(heap);
511 if (heap->cancelled_gc()) {
512 // Young generation bootstrap cycle has failed. Concurrent mark for old generation
513 // is going to resume after degenerated bootstrap cycle completes.
514 log_info(gc)("Bootstrap cycle for old generation was cancelled.");
515 return;
516 }
517
518 // Reset the degenerated point. Normally this would happen at the top
519 // of the control loop, but here we have just completed a young cycle
520 // which has bootstrapped the old concurrent marking.
521 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
522
523 // From here we will 'resume' the old concurrent mark. This will skip reset
524 // and init mark for the concurrent mark. All of that work will have been
525 // done by the bootstrapping young cycle. In order to simplify the debugging
526 // effort, the old cycle will ONLY complete the mark phase. No actual
527 // collection of the old generation is happening here.
528 set_gc_mode(servicing_old);
529 old_generation->transition_to(ShenandoahOldGeneration::MARKING);
530 }
531 case ShenandoahOldGeneration::MARKING: {
532 ShenandoahGCSession session(cause, old_generation);
533 bool marking_complete = resume_concurrent_old_cycle(old_generation, cause);
534 if (marking_complete) {
535 assert(old_generation->state() != ShenandoahOldGeneration::MARKING, "Should not still be marking.");
536 }
537 break;
538 }
539 default:
540 log_error(gc)("Unexpected state for old GC: %d", old_generation->state());
541 ShouldNotReachHere();
542 }
543 }
544
545 bool ShenandoahControlThread::resume_concurrent_old_cycle(ShenandoahGeneration* generation, GCCause::Cause cause) {
546
547 assert(ShenandoahHeap::heap()->is_concurrent_old_mark_in_progress(), "Old mark should be in progress");
548 log_debug(gc)("Resuming old generation with " UINT32_FORMAT " marking tasks queued.", generation->task_queues()->tasks());
549
550 ShenandoahHeap* heap = ShenandoahHeap::heap();
551
552 // We can only tolerate being cancelled during concurrent marking or during preparation for mixed
553 // evacuation. This flag here (passed by reference) is used to control precisely where the regulator
554 // is allowed to cancel a GC.
555 ShenandoahOldGC gc(generation, _allow_old_preemption);
556 if (gc.collect(cause)) {
557 generation->record_success_concurrent(false);
558 }
559
560 if (heap->cancelled_gc()) {
561 // It's possible the gc cycle was cancelled after the last time
562 // the collection checked for cancellation. In which case, the
563 // old gc cycle is still completed, and we have to deal with this
564 // cancellation. We set the degeneration point to be outside
565 // the cycle because if this is an allocation failure, that is
566 // what must be done (there is no degenerated old cycle). If the
567 // cancellation was due to a heuristic wanting to start a young
568 // cycle, then we are not actually going to a degenerated cycle,
569 // so the degenerated point doesn't matter here.
570 check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle);
571 if (_requested_gc_cause == GCCause::_shenandoah_concurrent_gc) {
572 heap->shenandoah_policy()->record_interrupted_old();
573 }
574 return false;
575 }
576 return true;
577 }
578
579 bool ShenandoahControlThread::check_soft_max_changed() const {
580 ShenandoahHeap* heap = ShenandoahHeap::heap();
581 size_t new_soft_max = Atomic::load(&SoftMaxHeapSize);
582 size_t old_soft_max = heap->soft_max_capacity();
583 if (new_soft_max != old_soft_max) {
584 new_soft_max = MAX2(heap->min_capacity(), new_soft_max);
585 new_soft_max = MIN2(heap->max_capacity(), new_soft_max);
586 if (new_soft_max != old_soft_max) {
587 log_info(gc)("Soft Max Heap Size: " SIZE_FORMAT "%s -> " SIZE_FORMAT "%s",
588 byte_size_in_proper_unit(old_soft_max), proper_unit_for_byte_size(old_soft_max),
589 byte_size_in_proper_unit(new_soft_max), proper_unit_for_byte_size(new_soft_max)
590 );
591 heap->set_soft_max_capacity(new_soft_max);
592 return true;
593 }
594 }
595 return false;
596 }
597
598 void ShenandoahControlThread::service_concurrent_cycle(ShenandoahGeneration* generation, GCCause::Cause cause, bool do_old_gc_bootstrap) {
599 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
600 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
601 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
602 // tries to evac something and no memory is available), cycle degrades to Full GC.
603 //
604 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
605 // heuristics says there are no regions to compact, and all the collection comes from immediately
606 // reclaimable regions.
607 //
608 // ................................................................................................
609 //
610 // (immediate garbage shortcut) Concurrent GC
611 // /-------------------------------------------\
612 // | |
613 // | |
614 // | |
615 // | v
616 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
617 // | | | ^
618 // | (af) | (af) | (af) |
619 // ..................|....................|.................|..............|.......................
620 // | | | |
621 // | | | | Degenerated GC
622 // v v v |
623 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
624 // | | | ^
625 // | (af) | (af) | (af) |
626 // ..................|....................|.................|..............|.......................
627 // | | | |
628 // | v | | Full GC
629 // \------------------->o<----------------/ |
630 // | |
631 // v |
632 // Full GC --------------------------/
633 //
634 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
635
636 ShenandoahHeap* heap = ShenandoahHeap::heap();
637 GCIdMark gc_id_mark;
638 ShenandoahGCSession session(cause, generation);
639 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
640
641 service_concurrent_cycle(heap, generation, cause, do_old_gc_bootstrap);
642 }
643
644 void ShenandoahControlThread::service_concurrent_cycle(const ShenandoahHeap* heap, ShenandoahGeneration* generation,
645 GCCause::Cause &cause, bool do_old_gc_bootstrap) {
646 ShenandoahConcurrentGC gc(generation, do_old_gc_bootstrap);
647 if (gc.collect(cause)) {
648 // Cycle is complete
649 generation->record_success_concurrent(gc.abbreviated());
650 } else {
651 assert(heap->cancelled_gc(), "Must have been cancelled");
652 check_cancellation_or_degen(gc.degen_point());
653 assert(generation->generation_mode() != OLD, "Old GC takes a different control path");
654 // Concurrent young-gen collection degenerates to young
655 // collection. Same for global collections.
656 _degen_generation = generation;
657 }
658 }
659
660 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
661 ShenandoahHeap* heap = ShenandoahHeap::heap();
662 if (!heap->cancelled_gc()) {
663 return false;
664 }
665
666 if (in_graceful_shutdown()) {
667 return true;
668 }
669
670 assert(_degen_point == ShenandoahGC::_degenerated_outside_cycle,
671 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
672
673 if (is_alloc_failure_gc()) {
674 _degen_point = point;
675 return true;
676 }
677
678 if (_preemption_requested.is_set()) {
679 assert(_requested_generation == YOUNG, "Only young GCs may preempt old.");
680 _preemption_requested.unset();
681
682 // Old generation marking is only cancellable during concurrent marking.
683 // Once final mark is complete, the code does not check again for cancellation.
684 // If old generation was cancelled for an allocation failure, we wouldn't
685 // make it to this case. The calling code is responsible for forcing a
686 // cancellation due to allocation failure into a degenerated cycle.
687 _degen_point = point;
688 heap->clear_cancelled_gc(false /* clear oom handler */);
689 return true;
690 }
691
692 fatal("Cancel GC either for alloc failure GC, or gracefully exiting, or to pause old generation marking.");
693 return false;
694 }
695
696 void ShenandoahControlThread::stop_service() {
697 // Nothing to do here.
698 }
699
700 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
701 ShenandoahHeap* const heap = ShenandoahHeap::heap();
702
703 GCIdMark gc_id_mark;
704 ShenandoahGCSession session(cause, heap->global_generation());
705
706 ShenandoahFullGC gc;
707 gc.collect(cause);
708
709 heap->global_generation()->heuristics()->record_success_full();
710 heap->shenandoah_policy()->record_success_full();
711 }
712
713 bool ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
714 assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
715 ShenandoahHeap* const heap = ShenandoahHeap::heap();
716
717 GCIdMark gc_id_mark;
718 ShenandoahGCSession session(cause, _degen_generation);
719
720 ShenandoahDegenGC gc(point, _degen_generation);
721 gc.collect(cause);
722
723 assert(heap->young_generation()->task_queues()->is_empty(), "Unexpected young generation marking tasks");
724 if (_degen_generation->generation_mode() == GLOBAL) {
725 assert(heap->old_generation()->task_queues()->is_empty(), "Unexpected old generation marking tasks");
726 assert(heap->global_generation()->task_queues()->is_empty(), "Unexpected global generation marking tasks");
727 } else {
728 assert(_degen_generation->generation_mode() == YOUNG, "Expected degenerated young cycle, if not global.");
729 ShenandoahOldGeneration* old_generation = (ShenandoahOldGeneration*) heap->old_generation();
730 if (old_generation->state() == ShenandoahOldGeneration::BOOTSTRAPPING && !gc.upgraded_to_full()) {
731 old_generation->transition_to(ShenandoahOldGeneration::MARKING);
732 }
733 }
734
735 _degen_generation->heuristics()->record_success_degenerated();
736 heap->shenandoah_policy()->record_success_degenerated();
737 return !gc.upgraded_to_full();
738 }
739
740 void ShenandoahControlThread::service_uncommit(double shrink_before, size_t shrink_until) {
741 ShenandoahHeap* heap = ShenandoahHeap::heap();
742
743 // Determine if there is work to do. This avoids taking heap lock if there is
744 // no work available, avoids spamming logs with superfluous logging messages,
745 // and minimises the amount of work while locks are taken.
746
747 if (heap->committed() <= shrink_until) return;
748
749 bool has_work = false;
750 for (size_t i = 0; i < heap->num_regions(); i++) {
751 ShenandoahHeapRegion *r = heap->get_region(i);
752 if (r->is_empty_committed() && (r->empty_time() < shrink_before)) {
753 has_work = true;
754 break;
755 }
756 }
757
758 if (has_work) {
759 heap->entry_uncommit(shrink_before, shrink_until);
760 }
761 }
762
763 bool ShenandoahControlThread::is_explicit_gc(GCCause::Cause cause) const {
764 return GCCause::is_user_requested_gc(cause) ||
765 GCCause::is_serviceability_requested_gc(cause);
766 }
767
768 bool ShenandoahControlThread::is_implicit_gc(GCCause::Cause cause) const {
769 return !is_explicit_gc(cause) && cause != GCCause::_shenandoah_concurrent_gc;
770 }
771
772 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
773 assert(GCCause::is_user_requested_gc(cause) ||
774 GCCause::is_serviceability_requested_gc(cause) ||
775 cause == GCCause::_metadata_GC_clear_soft_refs ||
776 cause == GCCause::_codecache_GC_threshold ||
777 cause == GCCause::_full_gc_alot ||
778 cause == GCCause::_wb_full_gc ||
779 cause == GCCause::_wb_breakpoint ||
780 cause == GCCause::_scavenge_alot,
781 "only requested GCs here");
782
783 if (is_explicit_gc(cause)) {
784 if (!DisableExplicitGC) {
785 handle_requested_gc(cause);
786 }
787 } else {
788 handle_requested_gc(cause);
789 }
790 }
791
792 bool ShenandoahControlThread::request_concurrent_gc(GenerationMode generation) {
793 if (_preemption_requested.is_set() || _gc_requested.is_set() || ShenandoahHeap::heap()->cancelled_gc()) {
794 // ignore subsequent requests from the heuristics
795 return false;
796 }
797
798 if (_mode == none) {
799 _requested_gc_cause = GCCause::_shenandoah_concurrent_gc;
800 _requested_generation = generation;
801 notify_control_thread();
802 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
803 ml.wait();
804 return true;
805 }
806
807 if (preempt_old_marking(generation)) {
808 log_info(gc)("Preempting old generation mark to allow %s GC.", generation_name(generation));
809 _requested_gc_cause = GCCause::_shenandoah_concurrent_gc;
810 _requested_generation = generation;
811 _preemption_requested.set();
812 ShenandoahHeap::heap()->cancel_gc(GCCause::_shenandoah_concurrent_gc);
813 notify_control_thread();
814
815 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
816 ml.wait();
817 return true;
818 }
819
820 return false;
821 }
822
823 void ShenandoahControlThread::notify_control_thread() {
824 MonitorLocker locker(&_control_lock, Mutex::_no_safepoint_check_flag);
825 _control_lock.notify();
826 }
827
828 bool ShenandoahControlThread::preempt_old_marking(GenerationMode generation) {
829 return generation == YOUNG && _allow_old_preemption.try_unset();
830 }
831
832 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
833 // Make sure we have at least one complete GC cycle before unblocking
834 // from the explicit GC request.
835 //
836 // This is especially important for weak references cleanup and/or native
837 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
838 // comes very late in the already running cycle, it would miss lots of new
839 // opportunities for cleanup that were made available before the caller
840 // requested the GC.
841
842 MonitorLocker ml(&_gc_waiters_lock);
843 size_t current_gc_id = get_gc_id();
844 size_t required_gc_id = current_gc_id + 1;
845 while (current_gc_id < required_gc_id) {
846 // Although setting gc request is under _gc_waiters_lock, but read side (run_service())
847 // does not take the lock. We need to enforce following order, so that read side sees
848 // latest requested gc cause when the flag is set.
849 _requested_gc_cause = cause;
850 _gc_requested.set();
851 notify_control_thread();
852 if (cause != GCCause::_wb_breakpoint) {
853 ml.wait();
854 }
855 current_gc_id = get_gc_id();
856 }
857 }
858
859 void ShenandoahControlThread::handle_alloc_failure(ShenandoahAllocRequest& req) {
860 ShenandoahHeap* heap = ShenandoahHeap::heap();
861
862 assert(current()->is_Java_thread(), "expect Java thread here");
863
864 if (try_set_alloc_failure_gc()) {
865 // Only report the first allocation failure
866 log_info(gc)("Failed to allocate %s, " SIZE_FORMAT "%s",
867 req.type_string(),
868 byte_size_in_proper_unit(req.size() * HeapWordSize), proper_unit_for_byte_size(req.size() * HeapWordSize));
869
870 // Now that alloc failure GC is scheduled, we can abort everything else
871 heap->cancel_gc(GCCause::_allocation_failure);
915 _do_counters_update.unset();
916 ShenandoahHeap::heap()->monitoring_support()->update_counters();
917 }
918 }
919
920 void ShenandoahControlThread::handle_force_counters_update() {
921 if (_force_counters_update.is_set()) {
922 _do_counters_update.unset(); // reset these too, we do update now!
923 ShenandoahHeap::heap()->monitoring_support()->update_counters();
924 }
925 }
926
927 void ShenandoahControlThread::notify_heap_changed() {
928 // This is called from allocation path, and thus should be fast.
929
930 // Update monitoring counters when we took a new region. This amortizes the
931 // update costs on slow path.
932 if (_do_counters_update.is_unset()) {
933 _do_counters_update.set();
934 }
935 }
936
937 void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
938 assert(ShenandoahPacing, "should only call when pacing is enabled");
939 Atomic::add(&_allocs_seen, words, memory_order_relaxed);
940 }
941
942 void ShenandoahControlThread::set_forced_counters_update(bool value) {
943 _force_counters_update.set_cond(value);
944 }
945
946 void ShenandoahControlThread::reset_gc_id() {
947 Atomic::store(&_gc_id, (size_t)0);
948 }
949
950 void ShenandoahControlThread::update_gc_id() {
951 Atomic::inc(&_gc_id);
952 }
953
954 size_t ShenandoahControlThread::get_gc_id() {
959 print_on(tty);
960 }
961
962 void ShenandoahControlThread::print_on(outputStream* st) const {
963 st->print("Shenandoah Concurrent Thread");
964 Thread::print_on(st);
965 st->cr();
966 }
967
968 void ShenandoahControlThread::start() {
969 create_and_start();
970 }
971
972 void ShenandoahControlThread::prepare_for_graceful_shutdown() {
973 _graceful_shutdown.set();
974 }
975
976 bool ShenandoahControlThread::in_graceful_shutdown() {
977 return _graceful_shutdown.is_set();
978 }
979
980 const char* ShenandoahControlThread::gc_mode_name(ShenandoahControlThread::GCMode mode) {
981 switch (mode) {
982 case none: return "idle";
983 case concurrent_normal: return "normal";
984 case stw_degenerated: return "degenerated";
985 case stw_full: return "full";
986 case servicing_old: return "old";
987 default: return "unknown";
988 }
989 }
990
991 void ShenandoahControlThread::set_gc_mode(ShenandoahControlThread::GCMode new_mode) {
992 if (_mode != new_mode) {
993 log_info(gc)("Transition from: %s to: %s", gc_mode_name(_mode), gc_mode_name(new_mode));
994 _mode = new_mode;
995 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
996 ml.notify_all();
997 }
998 }
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